Climate change will displace hundreds of millions of people by the end of this century, increasing the risk of violent conflict and wiping trillions of dollars off the global economy, a forthcoming UN report will warn.

The second of three publications by the UN’s Intergovernmental Panel on Climate Change, due to be made public at the end of this month, is the most comprehensive investigation into the impact of climate change ever undertaken. A draft of the final version seen by The Independent says the warming climate will place the world under enormous strain, forcing mass migration, especially in Asia, and increasing the risk of violent conflict.

Based on thousands of peer-reviewed studies and put together by hundreds of respected scientists, the report predicts that climate change will reduce median crop yields by 2 per cent per decade for the rest of the century – at a time of rapidly growing demand for food. This will in turn push up malnutrition in children by about a fifth, it predicts.

The report also forecasts that the warming climate will take its toll on human health, pushing up the number of intense heatwaves and fires and increasing the risk from food and water-borne diseases.

While the impact on the UK will be relatively small, global issues such as rising food prices will pose serious problems. Britain’s health and environmental “cultural heritage” is also likely to be hurt, the report warns.

According to the draft report, a rare grassy coastal habitat unique to Scotland and Ireland is set to suffer, as are grouse moors in the UK and peatlands in Ireland. The UK’s already elevated air pollution is likely to worsen as burning fossil fuels increase ozone levels, while warmer weather will increase the incidence of asthma and hay fever.

Coastal systems and low-lying areas

The report predicts that by the end of the century “hundreds of millions of people will be affected by coastal flooding and displaced due to land loss”. The majority affected will be in East Asia, South-east Asia and South Asia. Rising sea levels mean coastal systems and low-lying areas will increasingly experience submergence, coastal flooding and coastal erosion.

Food security

Relatively low local temperature increases of 1C or more above pre-industralised levels are projected to “negatively impact” yields of major crops such as wheat, rice and maize in tropical and temperate regions. The report forecasts that climate change will reduce median yields by up to 2 per cent per decade for the rest of the century – against a backdrop of rising demand that is set to increase by 14 per cent per decade until 2050.

The global economy

A global mean temperature increase of 2.5C above pre-industrial levels may lead to global aggregate economic losses of between 0.2 and 2.0 per cent, the report warns. Global GDP was $71.8trn (£43.1trn) in 2012, meaning a 2 per cent reduction would wipe $1.4trn off the world’s economic output that year.

Human health

Until mid-century, climate change will impact human health mainly by exacerbating problems that already exist, the report says. Climate change will lead to increases in ill-health in many regions, with examples including a greater likelihood of injury, disease and death due to more intense heatwaves and fires; increased likelihood of under-nutrition; and increased risks from food and water-borne diseases. Without accelerated investment in planned adaptations, climate change by 2050 would increase the number of undernourished children under the age of five by 20-25 million globally, or by 17-22 per cent, it says.

Human security

Climate change over the 21st century will have a significant impact on forms of migration that compromise human security, the report states. For example, it indirectly increases the risks from violent conflict in the form of civil war, inter-group violence and violent protests by exacerbating well-established drivers of these conflicts such as poverty and economic shocks.

Small-island states and other places highly vulnerable to sea-level rise face major challenges to their territorial integrity. Some “transboundary” impacts of climate change, such as changes in sea ice, shared water resources and migration of fish stocks have the potential to increase rivalry among states.

Freshwater resources

The draft of the report says “freshwater-related risks of climate change increase significantly with increasing greenhouse gas emissions”. It finds that climate change will “reduce renewable surface water and groundwater resources significantly in most dry subtropical regions”, exacerbating the competition for water. Terrestrial and freshwater species will also face an increased extinction risk under projected climate change during and beyond the 21st century.

Unique landscapes

Machair, a grassy coastal habitat found only in north-west Scotland and the west coast of Ireland, is one of the several elements of the UK’s “cultural heritage” that is at risk from climate change, the report says. Machair is found only on west-facing shores and is rich in calcium carbonate derived from crushed seashells. It is so rare and special, that a recent assessment by the European Forum on Nature Conservation and Pastoralism described it as an “unknown jewel”.

The IPCC also warns of climate threats to Irish peatlands and UK grousemoors and notes an increasing risk to health across Europe from rising air pollution – in which the polluted UK is already in serial breach of EU regulations.

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